What does "Always On" in BIOS Power settimgs do ?

Hi Experts, I need to know what "Always On" in a Server Motherbord's BIOS seting usually means.....
I know that it will soft switch "on" the power button when power is re-applied to the server after an outage ......
How will this seting act if the server is properly shut down ? Will it never cut the power to the motherboard ? if not then that all is good .......
if it does shut down all the way despite the BIOS setting of "allways on"....when I then cut the power to the server - will the server power on after I re-apply power ?

This is a major decison for me on how to buy and deploy UPS units to protect my servers from crashing - if I can't boot them back up after an extend outage (longer that the UPS can survive) then the UPS is no good to me....

Thnaks for helping !
gerdwilhelmiAsked:
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lancecurwensvilleCommented:
Depending upon the manufacturer, "always on" is a flag for power settings in terms of shutting off non-used devices to save power.  There may be a setting called "last power state" which refers to the systems ability to power back on in the event of a sudden power loss.  If the system is shut down properly, then this will have no effect when it turns back on.  If the UPS software appropriately shuts everything down, I believe that it must be manually powered back on.
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gerdwilhelmiAuthor Commented:
OK - thanks lancecurwensville !

 I was afraid somone who knows would say that....

Just to be extremely clear - here is what I intend to have happen :

- I set the BIOS Power state settting to "Always ON"
- I manually (or initiated by UPS SW) shut down the server properly
- I then disconect the power cable from the server (or shut down the UPS....)
- I then reconnect the power cable to the server (or restart the UPS - e.g. when the power comes back)

Now......will the server boot or not ???
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lancecurwensvilleCommented:
Just looked at some forum articles from APC (http://emea-en.apc.com/app/answers/detail/a_id/1191/~/ups-powers-off-but-computer-does-not-reboot-after-system-is-shutdown)  If the bios is set to always on, and APC software shuts it down, when power is restored, it WILL turn back on.  If you turn it off through windows, it will NOT turn back on.  Sorry if my first comment was inaccurate.
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Gary CaseRetiredCommented:
"... Depending upon the manufacturer, "always on" is a flag for power settings in terms of shutting off non-used devices  ..."   ==>  NO !!    This setting has nothing whatsoever to do with any other devices.

"Always On" means exactly what you're hoping it does -- it means when power is applied to the system, it should turn on.      This is exactly how you want a system set that has UPS power ... when power is lost, the UPS software causes a proper shutdown; then the UPS turns off.     When power is restored, the UPS restores power ... and the system turns on.
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andyalderSaggar maker's framemakerCommented:
There's always the option to use DontPowerOffAfterShutdown registry key (assuming it's Windows) if there isn't a BIOS setting to make it power on after being shut down, see the more info section of http://support.microsoft.com/kb/819760.
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Gary CaseRetiredCommented:
Andy ==>  This wouldn't achieve anything ... although it wouldn't hurt anything either.

All that key does is displays the "It is now safe to turn off your computer" message instead of actually turning it off.    In the case of a UPS-induced shutdown, the system would still lose power when the UPS turned off ... so it would still turn back on IF the power setting was "Always On".

I simply can't think of any reason you'd want to use that key.
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lancecurwensvilleCommented:
@garycase:  thank you for the better clarification.  I was incorrect with the statement I made, I attempted to correct myself in the second post.  Apologies to all.
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arnoldCommented:
To add with the setting to always on, the system will come back on when power is cycled event if the shutdown was initiated within windows (proper shutdown)
i.e. an error on an administrators part who remoted in and issued shutdown /t 30 forgetting the /r switch and resulted in a server shutdown.  cycling an RPC the the server connected through (UPS with opton to turn off supply ports), will turn the system on when power is sensed.
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gerdwilhelmiAuthor Commented:
lancecurwensville:
Your reference mentions an article from  2002.....not sure if that still aplies. I tend to go with arnold.........


Willm give hiwm the points until I probve him wrong (which will hopefully never happen)
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gerdwilhelmiAuthor Commented:
Great insight - if it holds up.....
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andyalderSaggar maker's framemakerCommented:
Gary, that key has saved the day many times when UPS shutdown turns the server off and then after power cycle it doesn't come back on again. Some BIOS doesn't have the option to always power on when power is applied.
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